This invention relates generally to transport refrigeration systems and, more particularly, to improving system efficiency and reducing fuel consumption of an onboard diesel engine powering components of the transport refrigeration system.
Mobile refrigerated cargo systems, such as refrigerated trucks, refrigerated trailers and intermodal refrigerated containers are commonly used to transport perishable cargo, such as, for example, produce, meat, poultry, fish, dairy products, cut flowers, and other fresh or frozen perishable products. Conventionally, transport refrigeration systems used in connection with mobile refrigerated cargo systems include a transport refrigeration unit having a refrigerant compressor, a condenser with one or more associated condenser fans, an expansion device, and an evaporator with one or more associated evaporator fans, which are connected via appropriate refrigerant lines in a closed refrigerant flow circuit. Air or an air/gas mixture is drawn from the interior volume of the cargo space by the evaporator fan(s) associated with the evaporator, passed through the airside of the evaporator in heat exchange relationship with refrigerant whereby the refrigerant absorbs heat from the air, thereby cooling the air. The cooled air is then supplied back to the cargo space.
Commercially available transport refrigeration systems include a prime mover, typically a diesel engine, for powering the refrigerant compressor and other components, such as the condenser fans and evaporator fans, of the transport refrigeration unit. On refrigerated trucks and refrigerated trailers, the transport refrigeration system, commonly referred to as a reefer, is mounted to the truck or trailer and includes a prime mover as an integral component. On intermodal containers, a genset is mounted to the transport refrigeration unit carried on the container for powering the refrigerant compressor and other components of the transport refrigeration unit whenever the container is not connected to an external power supply. The genset includes a prime mover and an electric generator powered by the prime mover.
Diesel engines used as prime movers on transport refrigeration systems generally have two operating speeds, that is a high RPM speed, such as 2200 RPM, and a low RPM speed, such as 1400 RPM. In operation, the diesel engine is operated at high speed during pulldown of the temperature within the cargo space to a desired temperature set point and at low speed during the temperature maintenance mode. During standstill, that is when the refrigerant compressor is not operating, the diesel engine is typically idling at low speed. The diesel engine is generally designed to meet the power needs of the transport refrigeration system during operation at maximum capacity, such as during the temperature pulldown mode, with efficient fuel consumption. Therefore, during the temperature maintenance mode and standstill mode, the diesel engine is operating at lower efficiency and with increased fuel consumption.